1. Field of the Invention
The present invention relates to acid cation exchange resins which have been modified to form substantially neutral metal salts thereof, which have been found to be superior catalysts for several processes.
2. Related Art
The acid cation exchange resins are well known and have a wide variety of uses. The resins are cation exchangers, which contain sulfonic acid groups, and which may be obtained by polymerization or copolymerization of aromatic vinyl compounds followed by sulfonation. Examples of aromatic vinyl compounds suitable for preparing polymers or copolymers are: styrene, vinyl toluene, vinyl naphthalene, vinyl ethylbenzene, methyl styrene, vinyl chlorobenzene and vinyl xylene. A large variety of methods may be used for preparing these polymers; for example, polymerization alone or in admixture with other monovinyl compounds, or by crosslinking with polyvinyl compounds; for example, with divinyl benzene, divinyl toluene, divinylphenylether and others. The polymers may be prepared in the presence or absence of solvents or dispersing agents, and various polymerization initiators may be used, e.g., inorganic or organic peroxides, persulfates, etc.
The sulfonic acid group may be introduced into these vinyl aromatic polymers by various known methods; for example, by sulfating the polymers with concentrated sulfuric and chlorosulfonic acid, or by copolymerizing aromatic compounds which contain sulfonic acid groups (see e.g., U.S. Pat. No. 2,366,007). Further sulfonic acid groups may be introduced into the polymers which already contain sulfonic acid groups; for example, by treatment with fuming sulfuric acid, i.e., sulfuric acid which contains sulfur trioxide. The treatment with fuming sulfuric acid is preferably carried out at 0 to 150 degrees C. and the sulfuric acid should contain sufficient sulfur trioxide so that it still contains 10 to 50% free sulfur trioxide after the reaction. The resulting products preferably contain an average of 1.3 to 1.8 sulfonic acid groups per aromatic nucleus. Particularly, suitable polymers which contain sulfonic acid groups are copolymers of aromatic monovinyl compounds with aromatic polyvinyl compounds, particularly, divinyl compounds, in which the polyvinyl benzene content is preferably 1 to 20% by weight of the copolymer (see, for example, German Patent Specification No. 908,247).
The ion exchange resin is generally used in a granular size of about 0.25 to 1 mm, although particles from 0.15 mm up to about 2 mm may be employed. The finer catalysts provide high surface area, but also result in high pressure drops through the reactor. The macroreticular form of these catalysts have much larger surface area exposed and limited swelling which all of these resins undergo in a non-aqueous hydrocarbon medium compared to the gelular catalysts.
The acid cation exchange resins have been widely used in etherifications and have recently been found to be useful for deetherifications and transetherifications. Other reactions known to be carried out with the aid of cation exchange resins include dimerizations, hydration of olefins, esterifications and epoxidations.
The modified cation exchange resin catalyst of the present invention have been found particularly useful for deetherifications, dehydration and hydration of organic compounds.
The modified catalysts of the present invention exhibit substantial improvement in thermal stability compared to the base resin, however, the catalysts continue to exhibit the properties of acid catalysts. Furthermore, the present catalysts have been observed to be more selective in reactions.
The simplicity and safety of the present process which produces the present high temperature, active resin type catalysts is an advantage over other types of stabilizations wherein the resins are chlorinated or brominated.